Changes

'''Half-life''' is the time it takes for half of the original sample of a [[radioactive]] [[isotope]] to decay.<ref>Wile, Dr. Jay L. ''Exploring Creation With Physical Science''. Apologia Educational Ministries, Inc. 1999, 2000</ref>  Different isotopes have different half-lives, some being very short and difficult for scientists to study.<ref>Avison J. ''The World of Physics''; Thomas Nelson and Sons; Cheltenham. p. 395, (1984) [http://books.google.com/books?id=DojwZzKAvN8C&lpg=PA395&dq=%22short%20half-life%22&pg=PA395#v=onepage&q=%22short%20half-life%22&f=false]</ref> If the [[exponential decay]] of a radioisotope is expressed as <math>A = A_0 e^{-(t-t_0)/\tau}</math>, then the half-life is equal to <math>\tau</math> ln 2.  Knowing these decay rates is important for dating, such as with [[carbon|carbon-14]].

'''Half-life''' is the time it takes for half of the original sample of a [[radioactive]] [[isotope]] to decay.<ref>Wile, Dr. Jay L. ''Exploring Creation With Physical Science''. Apologia Educational Ministries, Inc. 1999, 2000</ref>  Different isotopes have different half-lives, some being very short and difficult for scientists to study.<ref>Avison J. ''The World of Physics''; Thomas Nelson and Sons; Cheltenham. p. 395, (1984) [http://books.google.com/books?id=DojwZzKAvN8C&lpg=PA395&dq=%22short%20half-life%22&pg=PA395#v=onepage&q=%22short%20half-life%22&f=false]</ref> If the [[exponential decay]] of a [[radioisotope]] is expressed as <math>A = A_0 e^{-(t-t_0)/\tau}</math>, then the half-life is equal to <math>\tau</math> ln 2.  Knowing these decay rates is important for dating, such as with [[carbon|carbon-14]].

It should be noted that the measurement of half-life is based on ''recent'' observations, and the numbers that follow from radioactive dating based on nuclear decay extrapolate from this assumption. For example, if a sample of biological material has 1/4 of the Carbon-14 relative to the rate a similar biological material has, ''constant'' half-life extrapolation dates this sample as two half-lifes old (in the order of 11,000 years). The creationist blog [[Answers in Genesis]] suggests that half-life varies over time.<ref>[http://www.answersingenesis.org/articles/am/v1/n1/creation-research Raising the Bar on Creation Research - by Don DeYoung, Ph.D.]</ref> An analogy for this extrapolation would be taking the population growth of Germany today (a negative rate), extrapolating backwards, and concluding that there were 100 billion germans during the time of the fall of the Roman Empire.  

It should be noted that the measurement of half-life is based on ''recent'' observations, and the numbers that follow from radioactive dating based on nuclear decay extrapolate from this assumption. For example, if a sample of biological material has 1/4 of the Carbon-14 relative to the rate a similar biological material has, ''constant'' half-life extrapolation dates this sample as two half-lifes old (in the order of 11,000 years). The creationist blog [[Answers in Genesis]] suggests that half-life varies over time.<ref>[http://www.answersingenesis.org/articles/am/v1/n1/creation-research Raising the Bar on Creation Research - by Don DeYoung, Ph.D.]</ref> An analogy for this extrapolation would be taking the population growth of Germany today (a negative rate), extrapolating backwards, and concluding that there were 100 billion germans during the time of the fall of the Roman Empire.